TypeScript not able to iterate associative array

Question

I have a service which populates my associative array in typescript,

fun populateData(){
let tempArr;
tempArr = [];
this.service.get('Post', 1, 'true').subscribe(
        (response) => {
          this.loadingIcon = false;

          for (let i = 0; i < response.results.length; i++) {
             tempList = response.results[i]['tags'];
             for ( let iter of tempList){
               if ( iter in tempArr) {
                 tempArr[iter] = tempArr[iter] + 1;
               }else {
                 tempArr[iter] = 1;
               }
             }
          }
        },
        (error) => {
          if (error['status'] === 401) {
            localStorage.clear();
            this.router.navigateByUrl('/login');
          } else {
            this.router.navigateByUrl('/error');
          }
        }
      );
      console.log(tempArr);
        /*
          This function is inside a class, once I iterate get access to tempArr I will be assigning the tempArr data to a class variable like

       for (items in tempArr){
            this.data.push(items, tempArr[items]);
       }
        */
}

I'm able to populate my associative array with the service above which gives the following output in console,

I'm not able to iterate through this array, I tried a couple of methods like the following,

for ( const key in tempArr) {
      console.log(key + ':' + tempArr[key]);
    }

I want both they key and values from the array.

Is there a reason you're not using an object? They're made for this exact purpose. — Gustorn
– Gustorn, Commented Mar 19, 2018 at 18:33
@Gustorn I'm not sure of how to use object for this, any pointers will be of great help. — Dhananjayan Santhanakrishnan
– Dhananjayan Santhanakrishnan, Commented Mar 19, 2018 at 18:36
@Gustorn I've updated the question, with the tempArr declarations — Dhananjayan Santhanakrishnan
– Dhananjayan Santhanakrishnan, Commented Mar 19, 2018 at 18:46
you are not using array but rather plain object, and to iterate through all pairs of (key, value) you can use ES7 Object.entries method. — c69
– c69, Commented Mar 20, 2018 at 3:31

Gustorn · Accepted Answer · 2018-03-19 19:14:37Z

3

TypeScript generally assumes that the keys to arrays are numbers. What you were doing might work but it's not very idiomatic. I'm not going to rewrite your whole function but here are a few pointers:

When constructing your associative array (map for short from now on) you should try using an object instead of an array:

const tagCounts: { [key: string]: number } = {};
for (const result of response.results) {
    for (const tag of result.tags) {
        tagCounts[tag] = (tagCounts[tag] || 0) + 1;
    }
}

Then you can iterate the result with:

for (const tag of Object.keys(tagCounts)) {
    const count = tagCounts[tag];
    // Other stuff here
}

Or if you have polyfills for Object.entries then with:

for (const [tag, count] of Object.entries(tagCounts)) {
    // Other stuff here
}

Looking at your code, this.data.push also seems wrong: it will add a string and a number to your data array which is almost certainly not what you want. You might want to consider converting data to an object as well if you want to store key-value pairs.

edited Mar 19, 2018 at 19:14

answered Mar 19, 2018 at 19:03

Gustorn

4553 silver badges8 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Dhananjayan Santhanakrishnan Over a year ago

I tried this one, however while trying to iterate using Object.keys(tagCounts) it is not entering the for loop. I can see the data in the tagCounts object in console log, i tired printing Object.keys(tagCounts) which is printing an empty array of size zero.

Collectives™ on Stack Overflow

TypeScript not able to iterate associative array

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related